The present invention generally relates to a connector and, more specifically, to an optical fiber connector for coupling a pair of single optical fibers.
With the improvement of transmission loss in optical fibers, the Fresnel reflection caused on an optical fiber end surface in an optical fiber connector has been becoming a critical factor in the determination of the transmission quality of optical communication systems. More particularly, the feedback of reflected light to a laser diode makes the oscillation characteristics thereof unstable, and reflected light again returns to the light receiving element to deteriorate the S/N ratio.
In order to avoid Fresnel reflection, several arrangements have been attempted; (1) an index matching agent is inserted between end surfaces of two optical fibers; (2) the end surfaces of optical fibers are coated with a non-reflecting film (Jap. Utility Model Application Laid-open, 88217 (1981); and (3) either the end surfaces of the optical fibers or the end surfaces of the ferrule are inclined to make a reflection angle larger than the numerical aperture of optical fibers so as to leak light (refer to Jap. Patent Application Laid-open 149346 (1978) and 150142 (1979). The index matching agent and the non-reflection coating aim at reducing reflection per se while the slant configuration of the end surfaces has the intention of preventing propagation of reflected light.
The first means, however, lacks reliability, and is inconvenient in mating and/or disconnection. The second means is defective in that it is practically impossible to lower the refractive index of the coated films to less than 1%, and in that such coating might peel off when fibers are coupled in abutment. The third means is also disadvantageous in that end surfaces of the fibers must be bevelled accurately at a particular angle and, further, at the time of mating two fibers, and surfaces of each fiber should be accurately aligned anglewise.